The invention relates to a method of improving the reliability of a data-processing station by replication, and it is applicable to any data-processing system requiring a high level of operating reliability, e.g. to telecommunications networks which must be operational permanently.
In known manner, improving the reliability of such a system involves, in particular, duplicating the dataprocessing station. In this way, the system has an "active" station, in which the various pieces of software of the system are executed, and a "back-up" station. The system must be capable of switching over to the back-up station when the active station fails, the back-up station then becoming the active station.
Most replicated systems of this type share a common mass memory. However, such a configuration can be impossible, e.g. when the two stations are mutually remote, and cannot physically share the same peripherals. In which case, it is necessary to duplicate the station entirely including the mass memory, so that each of the two stations has its own mass memory.
In such a case, to enable the active station to be switched over to the back-up station in a manner transparent to the software applications, it is essential to have a mechanism for synchronizing the data contained in each of the two mass memories.
Unfortunately, when one of the two stations fails, the synchronization mechanism becomes impossible to implement. When the second station also fails, it is necessary, on re-starting, to elect as the active station that station which has the more recent data in its mass memory, i.e. the station that failed last, so as not to lose any information.